Components of the Corticotropin-Releasing-Factor (CRF) Signaling System in Snail Atria

The vertebrate CRF signaling system consists of corticotropin-releasing factor (CRF), two types of receptors to CRF (CRF-R1 and CRF-R2), and CRF-binding protein (CRF-BP). The aim of this study was to investigate the presence and localization of CRF, CRF-R2, and CRF-BP in the snail atrial neuroendocrine complexes, which include granular cells (GCs) and tightly connected nerve fibers and gliointerstitial cells. Immunofluorescence assay and immunogold electron microscopy using polyclonal antibodies against these proteins revealed immunoreactivity in the granules of all these cells. Western-blot analysis of the snailatria lysate using rabbit anti-CRF-R2 polyclonal antibodies revealed a specific band with a weight of 56 kids. These are the first data on the molecular weight of this receptor in mollusks. Furthermore, to clarify the possible functions of CRF in the neuroendocrine complexes, the hormone was added to GCs isolated from the snail atrium. The proportion of degranulated GCs after CRF addition almost doubled (45.5 vs. 24.5% in control, p < 0.05). The results indicate the presence of all three components of the CRF signaling system in the neuroendocrine complexes of snail atrium. In addition, their presence in both secretory and nervous components of the complexes suggests that the CRF signaling system participates in the nervous regulation of secretory activity of GCs and transfer of information from GCs to the CNS.